The problem of abating pollution in cities by their own solid municipal wastes is an extremely complex scientific-technical and socio-economic task. The specific problems include the fact that a large variety of pollutants may comprise the wastes, the fact that the waste products are produced by humans, and the fact that the quantities of these wastes are continuously increasing.
Economically the most attractive solution could be automated sorting of refuse with the subsequent recycling of a significant part of the refuse components into useful items of manufacture. However, such sorting is an extremely laborious, epidemically and toxically dangerous process allowing separation of no more than 30% of the refuse, as it is impossible to successfully separate out the bulk of the refuse. See Katys M. Dumps of Household Waste Products and Incinerate Factories—Sources of Dioxins. 25.11.2002 20:21 (www.svoboda.org).
Experience in Germany has shown, that recycling is economically expedient only for such materials as ferrous metals, aluminum, glass (depending on local conditions), and probably, paper and is completely unacceptable for plastic, packing materials, newspapers, waste products of electronics, linoleum, etc. (Steven P. Reynolds. The German Recycling Experiment and its lessons for United States Policy. Villanova Environmental Law Journal. Vol. V1, 1995, Number 1.). In the USA 30.6% of municipal solid waste is recovered through recycling (23.5%) and composting (7.1%) (U.S. EPA. Municipal Solid Waste in the United States. 2003 Facts and Figures). This figure of only 30$ means, that approximately 70% of solid waste be processed in a different way.
An emergency has developed all over the world concerning how to clean up oil containing waste products. Until now, a comprehensive solution to the problem, which includes—clearing of the ground repeatedly polluted with mineral oil (for example, decontaminating the ground in the area of gas stations, seaports, railway depots, tank farms, etc.), recycling of acid tars (waste products of sulfuric acid used in purification of some mineral oils, for example, lubricant oils, containing 15-70% of the sulfuric acid dissolved in water), cleaning up and removing ground sediments of oil tanks, ponds—sediment bowls, earthen sludge barns, forming a solid phase, containing paraffins, asphalt-resinous substances, sulfur, sand, clay and other mechanical impurities, and also heavy metals—lead, cadmium, zinc, etc. is not found. Such refuse is generally processed in a thermal neutralization plant where as a result of pyrolysis of the refuse, a dry carbon containing material is obtained useful as a raw material for the manufacture of building materials and asphalt concrete mixes, and also a condensate and a gas are obtained where the condensate and the gas used as fuel in these plants. See Zharov O. A., et al, Modern Russian Technologies. Vol. 2. Technologies and the Equipment for Processing and Recycling of Oil Containing Waste Products and Oil Sludges. The Directory. Ecoline. Yaroslavl, 2003). It is necessary to note that such a solution to the problem is not satisfactory as the solid residues of pyrolysis contain heavy metals and, hence, are not suitable for industrial use, and so a burial place for the residues is required. In addition it is impractical to extract oil from ground deposits in view of the high expenses and insignificant quantity of the oil phase: on the average 5-8%. A more rational way to solve the problem of how to clean up oil sludge would entail joint processing of residues of pyrolysis with municipal solid waste (Muzipov H. N., Nalobova E. V., Shantarin V. D. Utilization of Ground Sediment of Oil Tanks without Waste 21.01.2003 11:29/www.promeco.hl.ru). However, the questions associated with protecting the environment from pollution by heavy metals, polychlorinated dibenzodioxins, -furanes and -biphenyls also would still not be solved.
Throughout the world there are some technologies which jointly thermally process municipal solid waste and sludge deposits of the sewage formed in city sewage purification plants. As a result of jointly burning municipal solid waste and sewage sludge in furnaces of various designs with preliminary drying deposits obtained and a required return of chimney gases after drying the gases and deodorization of the gases in a furnace is provided (U.S. Pat. Nos. 4,753,181, 5,630,366, 6,412,428 and Kremer A. I. About Prospects of Joint Thermal Processing of Municipal Solid Waste and Deposits of Sewage. 26.11.2002 22:38/www.gke.wl.dvgu.ru). In connection with the increased content of heavy metals in sludge deposits of sewage, all of these technologies result in obtaining extremely dangerous slag and ashes which require a burial place. Furthermore chlororganic compounds contained in the solid waste result in environmental contamination by such compounds, in particular, polychlorinated dibenzodioxins, -furanes and -biphenyls.
Today throughout the world there are more than ten technologies for processing solid municipal and industrial wastes. The most widespread among them are thermal processes: burning, pyrolysis and gasification.
Burning the wastes cannot be considered as the most economically sensible or conservation-minded method as many organic substances which could be recovered and put to good use, are burnt with additional consumption of fuel—up to 265π (70 gal) of fuel per ton of burnt solid waste (Clarke, M. J., DeKadt, M., and Saphire D. Burning Garbage in the USA. Practice vs. State of Art. Inform Inc. 1991. p. 146-147). Furthermore existing plants for refuse incineration have a lot of drawbacks, the main drawback is that while incinerating the wastes, they form secondary extremely toxic waste products (polychlorinated dibenzodioxins, -furanes, and -biphenyls) which are exuded together with heavy metals in an environment with chimney gases, sewage and slag. See Marjorie J. Clarke: Environmental Scientist Resource Recovery and Waste Disposal Planning. Minimizing Emissions from Resource Recovery. New York City Department of Sanitation; International Workshop on Municipal Waste Incineration. Sponsored by: Environment Canada. Meridien Hotel, Montreal, Quebec. Oct. 1-2, 1987. Second Edition; and L. A. Fedorov. Dioxins as Ecological Danger: Retrospective and Perspective. M. Nauka, 1993.-266 p. (www.seu/cci/lib/books/dioksiny).
As burning waste products provides warmth, the desire to use it for heating was natural. So movement: “Waste-to-Energy” has appeared (U.S. Pat. No. 5,862,762, Everett B. Woodruff, Herbert B. Lammers, Thomas F. Lammers. Steam Plant Operation. 7-th Edition. Division of the McGraw-Hill Companies, 1998. Chapter 13. Waste-to-Energy Plants, p. 729-774 and Joseph A. Salvato Nelson L. Nemerow, Franklin J. Acardy. Environmental Engineering. 5-th Edition. John Wiley and Sons, Inc. 2003. Chapter 5. Solid Waste Management, p. 755-888). However, burning of solid waste for the purpose of obtaining heat to manufacture electric power results in even greater environmental contamination. Since electric power consumption is not constant, but has daily and seasonal peaks that accordingly result in fluctuations of the required waste product load for the combustion chambers of garbage incineration boilers and, as a result lead to incompletely burning the waste products and to an even greater emission of harmful substances with chimney gases, slag, ash and sewage. For technical reasons only (low-calorie fuel, ineffective generators, etc.) the cost of the electric power generated by using the heat produced in municipal refuse incineration plants is not competitive with the cost of the electric power generated by using the heat produced in heat power stations. The price of one kilowatt generated by the heat produced in heat power stations 1-3 cents, and generated by the heat produced in refuse incineration plants—11 cents. Furthermore in view of the laws in force for stabilization of the market price of electricity to consumers many organizations that generate electric power are obliged to sell electricity for 2 cents for 1 kilowatt resulting in enormous losses for refuse incineration plants. In addition the necessity of providing a burial place for slag and ash further renders these plants absolutely unprofitable, and so financial forecasts for their development are extremely adverse (The Wall Street Journal. Aug. 11, 1993, p. A1-A2).
Many companies progress from simply burning refuse to a two-level process including a stage of pyrolysis (decomposition of organic substances without access of oxygen) at rather low temperatures 450-800° C. of. Such processes are energetically more favorable than simple burning. As a result of pyrolysis, the products obtained are pyrolysis gas and a solid residue of pyrolysis. These products may be sent at once without any additional processing to a combustion chamber for burning. A part of the gases of pyrolysis after condensation can be removed from the system and used as a liquid fuel by other consumers (U.S. Pat. Nos. 4,485,745 and 5,669,317). However, the same drawbacks are observed as with the direct burning of waste products. In order to clear pyrolysis gas of acid gases such as chloride hydrogen (HCl), it is necessary to employ an expensive b process which becomes expensive because of the need to use expensive equipment and to use expensive caustic or calcinated soda. Furthermore environmental contamination by heavy metals is not eliminated.
An alternative to the process of pyrolysis is the process of gasification which proceeds similarly but at a temperature 800-1300° C. and in the presence of a small amount of air. In this case the obtained gas is a mixture of low-molecular hydrocarbons which is then burned in a furnace. Such a process does not improve the ecological situation because of the presence of air and the presence of chlorine-containing organic substances in the refuse, which in combination with high temperature results in intensive formation of chlorinated dioxins, furanes and biphenyls. In addition salts of heavy metals are not removed in the process and pollute the environment. See U.S. Pat. No. 5,445,087 and the Review of Modern Technologies of Reception of Liquid Fuel from Biomass by Fast Pyrolysis. 06.01.2003 21:59/www.sciteclibrary.com.
The most complete destruction of the environmentally hazardous products contained in refuse is carried out using high-temperature pyrolysis or gasification at a temperature of 1650-1930° C. fused in a mix of mineral additives with metal (U.S. Pat. No. 5,134,944), or at temperature up to 1700° C. (3100° F.) in a melt of salts or alkalis in a mix with additives and in the presence of catalysts (Ukraine Patent No 57984 A). The specified ways enable processing refuse of practically any composition as at such a temperature all dioxins, furanes and biphenyls are completely destroyed. As a result one obtains synthesis gas—a mix of hydrogen, methane, carbon monoxide, carbon dioxide, water steam, nitrogen oxides and sulfur, and a solid residue—coke, inorganic materials, namely, lime, cement, glass and slag which are poured out from the reactor in sealed bunkers. The solid residues form without any established industrial process for their further use and resulting in wasted melts of salts and metal whose regeneration is an extremely complex and power-intensive process requiring in addition a significant consumption of various reagents. Synthesis gas after enough complex decontamination can be used as fuel. It is necessary to note also that the specified processes do not provide removing of heavy metals and their salts from the solid residue of pyrolysis. Therefore any further application of slags obtained from those residues for manufacture of building materials and designs is impossible. Furthermore special measures on recycling the slags or a burial place are necessary.
The technology of processing of waste products on a basis of low temperature plasmas at 2000-100000° C. is applied basically to small volumes of especially dangerous waste products, for example, biologically polluted waste products of hospitals and differs from other technologies for processing wastes by the high cost of processing ($100 per ton of waste products) that practically excludes any real opportunity to apply this method on large industrial scales See Installation for Medical and Hazardous Waste Treatment Using the AC Plasma—Arc System Soliton—NTT with Institute of Problems of Electrophysics. http://soliton.msk.ru/hazard.html 12.21.2002.
The concentration of oxides of heavy metals in slag and ashes is 2-3 times (and sometimes more) higher than the concentration in burnt solid waste. Therefore, even though thermal methods allow considerably reducing the volume of waste products, the resulting ashes that are formed are even more dangerous to the environment and the slag formed requires special measures for recycling or a burial place. See Yufit S. S. Incinerate Factories—Rubbish Heap in the Sky Ecoline, 1998.
For processing of toxic slags the technology of ecological concreting is used: forming a mixture of slags after their neutralization with cement, lime or silicon dioxide with the subsequent hardening of the mix. If the waste products are correctly mixed with the cohesive agent “incapsulation” of the toxic substances occurs (including heavy metals and dioxins) in the cement stone which does not permit passing toxic substances into the environment. See U.S. Pat. Nos. 4,120,735, 4,518,508, 5,286,430, 5,466,407, 5,649,894 and 6,342,461. However, such technology requires preliminary neutralization of waste products employing several chemical reagents. A number of the substances forming waste products, for example, sulphur-containing substances can cause degradation of the cement stone that results in diffusion of contaminants into the environment. Besides, toxic metals under certain conditions can be washed away from the storage blocks by rains, for example, when there is a change of acidity of rain water according to “weather conditions”. SeeYufit S. S. Incinerate Factories—Rubbish Heap in the Sky. Ecoline, 1998.
An advanced method of ecological reconcreting, an integrated mineral-matrix technology, should provide ecological safety of the recovered material due to chemical bonding of contaminants down to their inclusion in a breaker plate creating a new cement formation (for example, heavy metals) or blocking of contaminants by colloid-disperse and sol-helium phases within the formed material. See U.S. Pat. Nos. 4,726,710, 4,741,776 and 4,872,954. However, it is possible only at rationally picked up components of system when potential chemical properties of components of system and their mechanical characteristics are established. See Knatko V. M., Knatko M. V., Scherbakova E. B. IMM—Technology Against Waste Products./Imitation of Natural Processes of Mineral Formation—a Perspective Direction of Neutralization and Recycling of Industrial Wastes. Energy: Economy, Technique, Ecology.—No 12, 2001, p. 29-35.
Commercially such condition cannot be established as the structure of the municipal refuse and accordingly of the slag is not constant. Thus, even the advanced technologies do not provide manufacture of non-polluting slag, suitable for further use. Furthermore the cost of a slag burial place is ten times higher than that of a burial place for municipal refuse.
It is necessary to note that in all patents which have been mentioned above directed to processes for hardening of slag-concrete mixes, it is stipulated that the temperature of the ambient air is the usual temperature. It is the extremely irrational to assume such an ambient temperature because it takes too long and reducing the ambient temperature forms turnaround delays in the release of finished goods. For acceleration hardening of concrete and for increasing physico—mechanical parameters of products, one must apply thermohumid processing—steaming in chambers by the wet saturated steam which creates the necessary thermal and damp inert environment, favorable for hardening of concrete. Modes of steaming are various and depend on the structure of concrete mixes, the optimum temperature for isothermal concrete warm up is 80-85° C., that provides after 8-20 hours the same durability which concrete obtains after aging for 28 days. See Bazhenov Y. M. Concrete Technology. Moscow, 1978, p. 205-229. However, such a way to reduce the production cycle, and to increase physico-mechanical parameters of products provides significant expenses for construction and operation of boiler-houses, the big charge of the steam reaching 1.2T on 1 m3 concrete and, accordingly, of water and fuel (Dmitrovich A. D. Heat and Mass Exchange at Hardening of Concrete in the Steam Environment. Moscow, 1967).
Fuel production by pyrolysis of waste products is extremely important. In many cases it possible to replace oil with fuel obtained by pyrolysis of waste products, or to use a mix of them. All known processes provide preliminary sorting and classification of waste products with the subsequent pyrolysis of an organic part at various temperature ranges: 200-600° C. (U.S. Pat. No. 5,114,541), 315-565° C. (U.S. Pat. No. 4,153,514), 400-870° C. (U.S. Pat. No. 4,063,903), 430-730° C. (800-1350° F.) (U.S. Pat. No. 4,077,847) and burning of the solid residue of pyrolysis in furnaces of various designs. All these processes, however, lead to environmental contamination by toxic salts of heavy metals and are not suitable for processing the waste products containing polyvinyl chloride and other chlorine-containing plastics in connection with formation of polychlorinated dioxins, furanes and biphenyls. Furthermore after separation of a condensate of pyrolitic gas into fuel and water phases, additional complex water treating steps are required before the water phase can be dumped into the environment.
Three-stage burning processes developed for coal-fuel oil mazut and coal-dust boilers by Japanese companies Mitsubishi Heavy Industries, Inc. and Hitachi—Zosen (Development of MACT—in Furnace NOx—Removal Process for Utility Steam Generators/Y.
Takahashi e. a. //Proceeding of the American Power Conference. 1982. Vol. 44, p. 402-412 and Three-Stage Combustion System for Pulverized Coal Developed for Commercial Use/Y. Sekiguchi e. a. //Hitachi—Zosen Technical Review, 1982. Vol. 43, p. 95-104) and also three-stage burning for combustible solid waste are known. See U.S. Pat. Nos. 5,205,227 and 5,307,746. These methods allow lowering considerably emission of nitrogen oxides. However, these methods require careful preliminary sorting of municipal refuse because the methods are unsuitable for burning the waste products containing linoleum, plastic, batteries, accumulators and other materials including chlororganic substances and heavy metals. The slag and final chimney gases obtained from these waste products contain highly toxic dioxins, furanes, biphenyl and heavy metals.
The development of modern economically effective technologies for the thermal processing of municipal and similar waste products is necessary for achieving the maximal recycling of secondary power resources and above all for preliminary heating and drying of highly damp and frozen together waste products.
In U.S. Pat. No. 4,859,177 a furnace is disclosed for burning combustible waste products having a rotational device divided into a zone of drying and a zone of burning. Such integration of zones in one device provides economy of capital expenses at the time of construction. However, optimum efficiency of the furnace is possible only if waste products of constant humidity are processed so that the degree of recirculation of the final chimney gases in the rotational device and the temperature in a zone of burning of the furnace are balanced and constant. In the case where highly damp or frozen waste products are the combustible waste, and also where the combustible waste products are of variable humidity, the burning becomes chemically unstable, the waste products incompletely burn and, accordingly, the charge of fuel and emission of harmful substances into the atmosphere as well as into the slag sharply grows.
In Russian Patent No. model—35,257 a unit for pyrolysis of household waste products is described where a chamber of preliminary drying is designed as a bunker supplied with ripper and gas burners is powered by gas from the decomposition of waste products for heating the bunker up to 150-200° C. However, heating the bunker with gas obtained from the decomposition of waste products by an open flame results in local overheating and, accordingly, premature decomposition or premature ignition of waste products is possible. Furthermore obtaining final chimney gases from burners without recycling of heat and which are dumped directly into the atmosphere additionally pollute the environment and lead to the overexpenditure of fuel.
U.S. Pat. Nos. 5,052,313, 5,080,581 and 5,285,581 describe a way of processing of waste products of high humidity including preliminary dehydration in a mechanical device with subsequent heating and drying in a multisection dryer by final chimney gases from a furnace at the beginning of the process without contact with the environment, and then by direct contact of chimney gases with the waste products. The liquid educed from waste products in the mechanical device, concentrates in the evaporator due to recycling of heat leaving a dryer as a gas-vapor mixture; the concentrate goes to a dryer, and chimney gases after clearing in a scrubber are dumped in a chimney. Such method allows saving fuel and to obtain over regular intervals a wide range of dried up waste products before their feeding to a burning stage. However, it is impossible, to process the waste products, containing salts of heavy metals and chlorine organic substances as it is impossible to dump them into the atmosphere with slags containing polychlorinated dioxins, furanes, biphenyls and salts of heavy metals, and the condensate obtained after cooling of the gas-vapor mixture from a dryer needs complex clearing before dumping into the water drain.
In U.S. Pat. No. 5,231,936. drying and burning of highly damp combustible waste products are disclosed. Drying is carried out by final chimney gases obtained from the furnace. Air from a bunker initially holding refuse moves by use of a fan to a furnace for burning waste products that simultaneously destroys a part of foul-smelling gases. Drying the combustible waste products with final chimney gases reduces the discharge of fuel, however, direct contact of the environment results in pollution of chimney gases by foul-smelling gases from the combustible waste product and other harmful substances which then together with chimney gases are dumped in an atmosphere because the cyclone established before the chimney, entraps only a dust and soot substances.
In U.S. Pat. No. 4,542,703 a unit for burning waste products of any humidity is described including subsequent treatment of the gases that flow from the furnace following drying and burning of waste products and the afterburning of in a chamber of products of incomplete combustion. Waste products move along an end face of the rotating furnace opposite to a burner and move towards to a stream of gases that provides in the beginning their drying, and then burning. Slag is unloaded from the furnace in the area of location of a burner, and chimney gases go in the afterburning chamber which burner provides a spiral stream of gases inside the chamber at a temperature of 1200° C. The afterburning chamber is established with the purpose of reduction of concentration of products of incomplete combustion including dioxins contained in the final chimney gases from the furnace that would enable burning the plastics and toxins in the chimney gases. However, in the Commoner's work (Commoner B. et al. Waste Management and Research 5:327-346, 1987) it is disclosed that upon inspection of incinerators it has been established that dioxins are formed during burning and that formation of them occurs also in a zone of cooling, therefore a rise in temperature at burning does not result to destruction of dioxins. It is established that emissions of products of incomplete combustion from a different sort of furnaces for combusting waste products do not decrease over changes of temperature from 700° C. up to 1600° C. (Trenholm A., Thurnay R. Proceedings of the Thirteen Annual Research Symposium. Cincinnati, Ohio: U.S. EPA Hazardous Waste Engineering Research Laboratory, EPA/600/9-87/015, Jule 1987). And, in addition, high temperatures result in increased volatility of components that lead to an increase in emissions of dangerous heavy metals. Thus, the method of reduction of concentration of dangerous substances by afterburning has no substantiation and is not capable to reduce emission of products of incomplete combustion and heavy metals.
U.S. Pat. No. 4,292,742 discloses a plant of preliminary drying of burnt fuel by a gas depleted in oxygen or other inert gas, for example, by nitrogen. The system of drying of fuel includes a circulating contour having a heater of air with a fluidized bed of cooled slag, a dryer with the fluidized bed of dried up fuel, a cyclone, a filter and a fan connected to one another by a system of pipelines. Effective operation of such a plant is possible only for materials homogeneous in composition, for example, fuel. For processing non-uniform, complex waste products in a composition where the municipal refuse has a high degree of ablation of light particles (a paper, a film, etc.), i.e. short residence time in the fluidized bed of a dried up material that will result having a final high moisture content of refuse, which will fast plug up the cyclone, the filter and the condenser with a damp material, which will stop the plant and require clearing to resume operation.
In U.S. Pat. No. 5,762,010 a way of processing waste products of any humidity is disclosed by providing preliminary heating of an intermediate heat-carrier (the ceramic spheres used simultaneously as the heat carrier and as the crushing agent), through utilization of heat from a process of pyrolysis with the subsequent separation of ashes from spheres in the punched part of a drum-type dryer. Then the specified spheres at a temperature of 750° C. are mixed with the initial waste products for drying them with simultaneous heating of air within a dryer. Steam is released from the waste products and mixes with hot air and moves to heat more of the initial waste products. A part of the gas of pyrolysis obtained without additional processing goes to a combustion furnace, and final chimney gases heat up the remaining part of gas of pyrolysis to a temperature of 750° C. which moves through the chamber of gasification for pyrolysis of waste products. Any surplus of the gas of pyrolysis is burnt in burners in the open air. However, this method is suitable only for processing of industrial residue with a content of dry substances no more than 10% when formed ashes is easily coarsely ground by spheres and then is eliminated on screens. Such processing of municipal waste products forms a stable fine grind slag and, accordingly, its separation on screens from the spheres is impossible so that what must often result is a stoppage of the equipment for cleaning. Use of surplus of gas of pyrolysis is not stipulated as a commodity fuel therefore; it is completely burnt in burners in the open air, wasting the energy content, and in addition, its combustion pollutes the environment, so that chemical neutralization of steam condensate from the dryer is necessary before dumping the condensate down a water drain. In addition processing waste products containing chlororganic substances and heavy metals, inevitably results in environmental contamination by dioxins, furanes, biphenyls and salts of heavy metals.
In U.S. Pat. No. 4,797,091 preliminary drying is provided of an organic part of sorted crushed waste products by air which has been heated up through recovery of heat from slag leaving a rotational furnace. The system of drying of waste products utilizes a circulating contour including a cooler of slag, a crusher of waste products, a pneumatic dryer and a cyclone connected among themselves by system of pipelines. Drying of waste products is carried out by direct contact with hot air in a vertical pipe of a pneumatic dryer. However, in plant removal of moisture from the heat-carrier or preliminary heating of cold damp refuse is not provided, so that upon their direct contact the temperature of the air can be reduced to its dew-point temperature which will result in drainage of air due to loss of condensate and, accordingly, to humidifying instead of drying of refuse. In the case of an increase of the flow of the hot air which excludes cooling the hot air to its dew-point temperature, consumption of the electric power for blasting sharply increases which is inherent in the operation of pneumatic dryers. Besides, to adjust the duration of drying and final moisture content of dried up refuse is practically impossible. Therefore non-uniformly dried up waste products enter into a reactor of pyrolysis that, accordingly, result in the overexpenditure of fuel in the pyrolysis process.
Thus, the problem of preliminary drying of municipal and similar waste products before their delivery for thermal processing has no satisfactory solution.
In U.S. Pat. Nos. 4,353,713, 4,448,558 and 4,597,771 processing of coal together with a light fraction of the municipal solid waste is described including preliminary sorting and crushing of the specified waste products their mixing with limestone, pyrolysis of the obtained mixture with the subsequent clearing of pyrolitic gas, allocation of some products, burning of the rest and use of heat of exothermal reactions between limestone or dolomite and carbon dioxide. These processes, however, lead to environmental contamination by toxic salts of heavy metals and are not suitable for processing of waste products of plastic, despite that limestone or dolomite could neutralize the hydrogen chloride discharged following decomposition of plastic hydrogen chloride (HCl). The calcium chloride recovered through such neutralization (CaCl2) under conditions of high temperature in a gasifier 650-980° C. is in a melted condition (the melting temperature of CaCl2 is 737-747° C. that results in sintering and lumping of processable waste products, in a sharp decrease of efficiency of contact with the environment so that the process of neutralization of hydrogen chloride is absolutely not effective and, hence, practically excludes any possibility of processing of plastic. The high temperature in the furnace 1090-1315° C. results in a fused product of salts of heavy metals, in general chlorides and sulfates, (temperature of fusion 242-915° C., and, above their surface exist in equilibrium with these melts their vapors. As the partial pressure of the vapors of these salts is not enough, they wind up in chimney gases carried away from the furnace in a chimney, and, due to their low concentration it is practically impossible to separate them from the gases though their total proportion in the gases represents a serious environmental issue. In slag also there are salts of heavy metals that exclude any opportunity of its further use.
In U.S. Pat. No. 6,202,577 processing of municipal and similar waste products is disclosed including removal from them of large metal objects followed by crushing and mixing with limestone. Pyrolysis of the specified mixture is carried out in two stages. The first stage is carried out—in a mixer located in a furnace, at a temperature of 240-260° C. and which includes heat recycling of part of the solid residue of pyrolysis when chlororganic compounds which are found in the refuse, decay with n liberation of hydrogen chloride (HCl) which reacts with crushed limestone and thus is led out from the process. The second stage is carried out at a temperature of 450-500° C. and includes utilization of heat from the chimney gases obtained from a combustion chamber located below. Thus polychlorinated dioxins, furanes and biphenyls are not formed in volume in the furnace because all chlorine has been removed from processable refuse at the previous stage of pyrolysis. Gas liberated during pyrolysis is condensed, and the organic portion of it, is liquid fuel and goes together with non-condensed gases to a combustion chamber. The water phase is fed to a stage for washing out salts of heavy metals and calcium chloride (CaCl2) which formed by neutralization of hydrogen chloride (HCl). The washed out part of the solid products of pyrolysis after drying by mixing the solid products with hot slag is fed to a combustion chamber for burning. As a result the obtained slag does not contain heavy metals and sulfur. The preceding process has a number of essential disadvantages:
1. A process for preliminary drying of municipal refuse is not anticipated. It is known that a process of pyrolysis begins only then when water is completely evaporated and the temperature has achieved a critical value where decomposition of organics contained in the refuse takes place. This time period is a function of the humidity of the refuse at the beginning of the process and can take up to 30-40% of the length of the residence time of a waste material in the furnace of pyrolysis. Thus, the presence of moisture in refuse results in an increase in the residence time of waste products in the furnace of pyrolysis that essentially reduces its productivity, results in the overcomsumption of fuel and, accordingly, reduction in the out put of commodity fuel.
2. The municipal refuse contains different objects and materials including glass; the temperature interval at the beginning of its softening depends on the refuse composition, and is equal to 400-600° C. (750-1110° F.). Thus, cooling of slag using air having a temperature below the temperature specified will result in glass-transition and slagging of slag in the cooler and, accordingly, in a stoppage of work in the whole factory. Slag cooling at a temperature higher than the required temperature wastes a significant part of heat which results in the over-consumption of fuel in the combustion chamber and, accordingly, in a reduction of the output of fuel which can be marketed.
3. The solid products of pyrolysis after washing out in a scrubber have high humidity that require a large consumption of heat from the hot slag used for drying the solid particles in a mixer before feeding to a burning stage. As a result a significant amount of slag is recycled as ballast to the combustion chamber which complicates the burning out of combustible components of the solid product of pyrolysis, and results in the over-consumption of fuel and, accordingly, reduction of the output of fuel which can be marketed.
4. The manufacture of finished articles from slag is not a practical goal, which considerably reduces economic parameters of operation of the plant.
5. With the use of limestone during pyrolysis of municipal refuse to undergo a neutralization reaction with hydrogen chloride it is impossible to exclude a neutralization reaction with organic acids as well. Therefore to recover organic acids including acetic acid in significant quantities is impossible. In this connection instead of recovering organic acids it is more rational to carry out the pyrolysis to obtain liquid hydrocarbonic fuel.
6. The water contained within the damp refuse is removed during the process. Due to evaporation of a plenty of water in dryers of calcium chloride and dump water steams together with final chimney gases into an atmosphere the given technology has no sewage, however, a significant amount of additional fresh water is needed for cooling of slag by heat exchange with cool water before sending the slag to the consumer.
7. During neutralization of hydrogen chloride with limestone in the furnace of pyrolysis, calcium chloride is formed which then together with salts of heavy metals is extracting using wash water. After drying a part of this solution dry calcium chloride is obtained together with a concentrate of salts of heavy metals. Such a mixture is not a marketable product, it is necessary to first separate the calcium chloride from the heavy metals.
8. A complex and expensive preliminary clearing of harmful impurities (acids, sulfur compounds, etc.) is necessary for producing of liquid carbonic acid from gases of pyrolysis using chemical sorbents with subsequent clearing of the gas in electrofilters or by compressing the gas under high pressures with subsequent condensation and separation of impurities that renders production of carbonic acid economically unfavorable and, accordingly, does not reduce emission of carbon dioxide (CO2) into the atmosphere.
9. The joint burning in combustion chamber of liquid fuel, noncondensed gases of pyrolysis and solid products of pyrolysis is executed inefficiently what leads to significant emissions of nitrogen oxides into the atmosphere.
10. Direct contact between wash water and noncondensed gases of pyrolysis in a scrubber because of a difference in partial pressure of light organic substances in water and gas in the beginning results in enrichment by organic substances of the gas phase fed to combustion chamber, i.e. to blowing waters from light organic substances. Then taking into account that the quantity of these gases is not enough and also that in the gases there are products of incomplete condensation of organic substances that will collect and that will result in obtaining in a dryer calcium chloride water phase with an increased content of organic substances which, accordingly, will start the emissions of organic substances through a chimney as chimney gases into the environment.
11. For carrying out the process of pyrolysis the rotating drum furnace, including built—in devices for return of a part of a solid product of pyrolysis to the beginning of process and its mixture with an additional mix of waste products and with limestone is used. Such complex design of the furnace creates difficulties while in service including the need for stoppages for cleaning and repair.
Thus, for creation of the advanced highly effective technology and a plant for processing municipal and similar waste products it is necessary to exclude all drawbacks specified in the previous patents as discussed hereinabove.